28 THE VOYAGE OF H.M.S. CHALLENGER. 



The genus Pleurogonium (formerly termed by Sars Pleuracantha) was founded on 

 specimens from the Christiania Fjord, living at a depth of 10 to 15 fathoms. Since the first 

 description of the genus published in 1865, Dr. G. 0. Sars has described the new species 

 Pleurogonium inerme 1 and Pleurogonium spinosissimum, 3 the type species of the genus 

 being Pleurogonium rubicundum. These are all shallow-water forms, not ranging 

 apparently below 100 fathoms. 



The genus Pleurogonium comes near to Munna in structure, and it is also closely 

 allied to Leptaspidia, and to the remarkable genus Dendrotion, lately described by Sars ; 

 it is more particularly related to these two latter genera, with which it agrees in theuniun- 

 guiculate character of the thoracic limbs, those appendages being in Munna biunguiculate ; 

 the absence of eyes is also a character which Pleurogonium shares with Dendrotion and 

 Leptaspidia; there is, however, no possibility of confounding it with either; in 

 Leptaspidia the uropoda are uniramous and one-jointed, while in Dendrotion they have 

 altogether disappeared; these appendages in Pleurogonium, though rudimentary, arc 

 more developed than in Leptaspidia, consisting as they do of two rami. The articulation 

 of the antennary organs of Leptaspidia, below the cephalic shield, is another among the 

 many characters which distinguish the genus from Pleurogonium. 



The Challenger obtained three specimens, which appear to be the types of as many 

 new species, belonging to this genus. Two of them, which are described below under the 

 names of Pleurogonium albidum and Pleurogonium serratum, evidently come very near 

 to Sars's Pleurogonium rubicundum, with which they agree in the lateral spines of the 

 anterior thoracic segment; in the latter species, however, the posterior segments of the 

 thorax are not furnished with such spines, which are present in my own species. The 

 anterior prolongation of the head in Pleurogonium rubicundum is not found in the two 

 Kerguelen species. 



The third new species to be described in the present Report is Pleurogonium minutum, 

 which comes nearest to Sars's Pleurogonium inerme, being like it without the spiny 

 processes of the epimera ; an obvious point of difference between the two species is the 

 long lateral processes of the head in Pleurogonium minutum, which are not present in 

 Pleurogonium inerme. 



Pleurogonium albidum, F. E. Beddard (PL III. figs. 7-13). 



Pleurogonium albidum, F. E. Beddard, Proc. ZooL Soc. Lond., 1SS6, pt. i. p. 101. 



The following description of this species is based upon a single female example from 

 Kersmelen, measuring; about 3 mm. in length. 



The general shape of the body is much like Pleurogonium rubicundum ; that is, the 



1 Forhandl. Videmk. Selsk., 1882, No. 18, p. 67. 



2 Beretning om i Sommeren, 1865, foretagen Zoologisk Reise, p. 30 ; Archil- f. Math, og Katurv., 1S77, p. 352. 



